The invention relates to an optoelectronic device for acquiring images of planes, such as bar code, area code, matrix or stacked code symbols.
At present there are two large groups of optoelectronic devices for reading bar codes and other symbols which each have their own advantages: CCD reading devices and laser reading devices.
CCD reading devices comprise, in the first instance, a lighting system generally consisting of high-intensity light-emitting diodes arranged so as to illuminate the bar codes. These devices also comprise a lens for forming the image of the bar code on the light-sensitive elements of the CCD for a pause time known as integration time. After this integration time, a clock emits a transfer signal "PHgr"TG controlling the transfer of information contained in the light-sensitive elements of the CCD to an analogue shift register. A second clock then delivers a pixel signal "PHgr"pix which controls the sequential reading of the code image. During this sequential reading, a further image can thus be exposed in the light-sensitive elements of the CCD.
This type of CCD reading device has two main advantages. Firstly, the scanning of the image is entirely electronic and therefore does not require a moving part. Furthermore, this CCD technology allows high reading speeds for a cost price lower than that of laser technology devices.
Laser reading devices, for their part, firstly comprise a source, generally a laser diode, of emission of a laser beam which is focused by an optical system. They also comprise a mechanism of rotating or oscillating mirrors for deflecting the laser beam so that it describes annular scanning which forms an elementary scanning line when projected on the bar code. These devices also comprise an electro-optical system positioned so as to intercept the beginning of scanning and to emit a pulse representative of the beginning of the line to enable the decoding system to be synchronized. With this technology, the laser light reflected by the bar code is collected either by tracing the reverse path of the incident beam or by stationary global retro-collection, and directed toward a light-sensitive system such as a photodiode which creates an instantaneous electrical signal, that is without accumulation of charges, representative of the image of the bar code.
This type of laser reading device has the advantage of offering a greater depth of field and insensitivity to movement, in particular when the device is displaced perpendicularly to the bars of the code.
The differences in design of these two types of optoelectroric device, in particular with respect to processing of the image, mean that there are currently two completely different ranges of products belonging to each of the two families.
It is the object of the present invention to provide an optoelectronic device designed to allow the reading and decoding of images issuing either from a CCD type read head or a laser type read head.
To this end, the invention relates to an optoelectronic device for acquiring images of sprite planes, such as bar code symbols. In one aspect an opto-electronic device, comprises:
a lighting source capable of emitting an incident light beam,
an electronic sensor for acquiring images,
optics for forming images on the electronic sensor; and
a processor for reading and decoding the images acquired by the sensor and comprising a clock adapted to emit a transfer signal "PHgr"TG of each image acquired by said sensor.
In another aspect, the device comprises:
deflecting means for the incident beam comprising oscillating or rotating cyclic deflector driven by a driver for causing said cyclic deflector to oscillate or rotate in such a way that the incident beam describes, during each cycle, angular scanning adapted to generate at least one elementary scanning line on the plane,
a closed loop control circuit for controlling the driver coupled, on the one hand, to the clock in order to receive the transfer signal "PHgr"TG and, on the other hand, to said driver and adapted to synchronize the beginning of each scanning cycle in phase and frequency with the signal "PHgr"TG emitted by the clock.
The invention therefore involved substituting a module for reading symbols such as bar codes with a laser beam designed to be controlled by the processor of a CCD technology reader for the electro-optical assembly of a CCD technology bar code reader (CCD strip, lens, lighting).
To this end, the device according to the invention comprises closed loop control circuit for controlling the laser beam-type read module on the basis of the available transfer signal "PHgr"TG so as to supply an analogue signal comparable to the one originating from a CCD sensor which can therefore be processed and decoded by CCD technology processing means.
Starting with a single base incorporating CCD technology processing means, the concept of the invention therefore offers two groups of optoelectronic devices involving CCD and laser technology.
According to a first advantageous variation of the invention:
the cyclic deflector can take the form of a rotating polygon having n reflective facets,
the driver can take the form of a stepper motor coupled to rotate or oscillate the rotating polygon, said motor having a number of steps per revolution equal to kn, wherein k=x or 1/x, x being an integer,
the closed loop control circuit can take the form of a sequential controller coupled to the stepper motor to produce control phases of said stepper motor synchronized with the signal "PHgr"TG emitted by the clock.
According to this variation employing a rotating polygon, the use of a stepper motor eliminates the constraint of closed loop speed control. Furthermore, the provision of a motor with a number of steps which is a multiple or sub-multiple of the number of facets of the polygon eliminates the constraint of closed loop phase control and allows the beginning of scanning to be detected. An extremely simple sequential controller is therefore sufficient to produce the phases of control of the step-by-step motor on the basis of a single transfer signal "PHgr"TG.
The controller can therefore advantageously consist of sequential electronics comprising flip-flops for generating two phases of control of the stepper motor.
Furthermore, to ensure that the video signal and the transfer signal "PHgr"TG are in phase, the device according to one aspect of the invention advantageously comprises means for prior adjustment of the angular position of the body of the step-by-step motor.
To this end, the body of the stepper motor is advantageously sandwiched between two stationary elements in which the bearings of said stepper motor are rotatably mounted, the adjustment means comprising means for fixing the body of said motor to at least one of said stationary elements after prior adjustment of the angular position of said body.
In addition, according to an advantageous embodiment, the axis of rotation of the polygonal mirror is inclined to the edges of the facets by an angle xcex1 adapted such that each facet creates a shifted scanning line parallel to that created by the adjacent facets.
This arrangement allows the scanning lines generated by each facet to be shifted in a very simple manner so that the code can be scanned in a direction parallel to the bars of the symbol.
The angle xcex1 of inclination of the axis of rotation of the rotating polygon is advantageously substantially equal to one quarter of the angle subtended by the edges delimiting a facet.
According to a second advantageous variation relating to a device comprising, conventional CCD technology, a clock emitting a pixel signal "PHgr"pix for sequential reading of each image acquired by the sensor, wherein:
the cyclic deflector can take the form of an oscillating mirror coupled to the driver to oscillate the cyclic deflector with a predetermined amplitude between two extreme positions,
the closed loop control circuit of the driver comprises:
a counter incremented by the signal "PHgr"pix for sequential reading and adapted to be reset to zero during the emission of a transfer signal "PHgr"TG,
a comparator configured to compare the value of the counter with a stored value obtained by prior learning and representative of the phase displacement required to obtain the phase synchronization of the beginning of each scanning cycle with the signal "PHgr"TG, said comparator emitting a phase synchronization signal when the stored value corresponds to the value in the counter,
a controller coupled to the driver and receiving the transfer signal "PHgr"TG and the phase synchronization signal and adapted to synchronize said driver with said transfer signal "PHgr"TG.
According to this variation employing an oscillating mirror, the transfer signal "PHgr"TG is used to control the phase and speed of the oscillations of said mirror.
Moreover, the pixel signal "PHgr"pix associated with the counter and the comparator allows the phasing of the video signal and the transfer signal "PHgr"TG on the basis of a stored phase displacement value obtained in a prior learning phase.
Furthermore, according to this variation, the controller for the driver advantageously comprise electronics containing flip-flops D for generating oscillating mode control signals for the driver.
Further characteristics, aims and advantages of the invention will emerge from the following detailed description given with reference to the accompanying drawings which show non-limiting examples of a preferred embodiment of a laser technology read module according to the invention as well as three variations of closed loop control circuit according to various aspects of the invention.